Fluorocarbon molecules for high aspect ratio oxide etch

ABSTRACT

Etching gases are disclosed for plasma etching channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, etc., in Si-containing layers on a substrate and plasma etching methods of using the same. The etching gases are trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutene; hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane (1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-); or hexafluorocyclobutane (cis-1,1,2,2,3,4). The etching gases may provide improved selectivity between the Si-containing layers and mask material, less damage to channel region, a straight vertical profile, and reduced bowing in pattern high aspect ratio structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/439,831, filed Apr. 30, 2015, which is a 371 of International PCTApplication No. PCT/US2013/067415, filed Oct. 30, 2013, which claimspriority to U.S. application No. 61/720,139, filed Oct. 30, 2012, theentire contents of each being incorporated herein by reference.

TECHNICAL FIELD

Etching gases are disclosed for plasma etching high aspect ratio channelholes, gate trenches, staircase contacts, capacitor holes, contactholes, etc., in Si-containing layers on a substrate. Plasma etchingmethods of using the same are also disclosed.

BACKGROUND

In memory applications in the semiconductor industries, such as DRAM and2D NAND, plasma etching removes silicon-containing layers, such as SiOor SiN layers, from semiconductor substrates. For novel memoryapplications, such as 3D NAND (US 2011/0180941 to Hwang et al.), highaspect ratio etching of stacks of multiple SiO/SiN or SiO/poly-Si layersis critical. Preferably, the etchant has high selectivity between themask and layers being etched. Furthermore, the etchant preferably etchesthe structure such that the vertical profile is straight with no bowing.The 3D NAND stack may include other silicon containing layers.

Traditionally, plasma etching is carried out using a plasma source whichgenerates active species from a gas source (such as hydrogen-, oxygen-,or fluorine-containing gases). The active species then react with theSi-containing layers to form a fluorocarbon blocking overlayer andvolatile species. The volatile species are removed by low pressure inthe reactor, which is maintained by a vacuum pump. Preferably, the maskmaterial is not etched by the active species. The mask material maycomprise one of the following: photoresist, amorphous carbon,polysilicon, metals, or other hard masks that do not etch.

Traditional etch gases include cC₄F₈ (Octafluorocyclobutane), C₄F₆(Hexafluoro-1,3-butadiene), CF₄, CH₂F₂, CH₃F, and/or CHF₃. These etchgases may also form polymers during etching. The polymer acts asprotection layers on the sidewalls of the pattern etch structure. Thispolymer protection layer prevents the ions and radicals from etching thesidewalls which could cause non-vertical structures, bowing, and changeof dimensions. A link between F:C ratio, SiO:SiN selectivity, andpolymer deposition rate has been established (see, e.g., Lieberman andLichtenberg, Principles of Plasma Discharges and Materials Processing,Second Edition, Wiley-Interscience, A John Wiley & Sons Publication,2005, pp. 595-596; and FIG. 5 of U.S. Pat. No. 6,387,287 to Hung et al.showing an increased blanket selectivity to nitride for lower values ofthe F/C ratio).

Traditional dry etch methods, such as chemical etching, may not providethe necessary high aspect ratio (>20:1) because the high pressureconditions required during chemical etching may have detrimental effectson the aperture formed. Traditional chemistries, such as C₄F₈ and C₄F₆,may also be insufficient to provide the high aspect ratio requiredbecause the etch manufacturers are rapidly depleting the availableparameters used to make the traditional chemistries work, such as RFpower, RF frequency, pulsing schemes and tuning schemes. The traditionalchemistries no longer provide sufficient polymer deposition on highaspect ratio side walls during the plasma etching process. Additionally,C_(x)F_(y), wherein x and y each independently range from 1-4, polymerson sidewalls are susceptible to etching. As a result, the etchedpatterns may not be vertical and structures may show bowing, change indimensions, and/or pattern collapse.

One key issue with etching of patterns is bowing. Bowing is often due tosidewall etching of the mask layer, which is often an amorphous carbonmaterial.

Amorphous carbon materials can be etch by oxygen radicals in the plasmawhich can cause increased opening of the mask and result in a bow-likeetch structure.

U.S. Pat. No. 6,569,774 to Trapp discloses a plasma etch process forforming a high aspect ratio contact opening through a silicon oxidelayer. Trapp discloses inclusion of nitrogen-comprising gases such asNH₃ to fluorocarbon (C_(x)F_(y)) and fluorohydrocarbon (C_(x)F_(y)H_(z))etch chemistries to improve resist selectivity and reduce striations. Alist of 35 fluorocarbon and fluorohydrocarbon chemistries are disclosed,but no structural formulae, CAS numbers, or isomer information areprovided.

WO2010/100254 to Solvay Fluor GmbH discloses use of certainhydrofluoroalkenes for a variety of processes, including as an etchinggas for semiconductor etching or chamber cleaning. Thehydrofluoroalkenes may include a mixture of at least one compoundselected from each of the following groups a) and b):

-   -   a) (Z)-1,1,1,3-tetrafluorobut-2-ene,        (E)-1,1,1,3-tetrafluorobut-2-ene, or        2,4,4,4-tetrafluorobut-1-ene, and    -   b) 1,1,1,4,4,4-hexafluorobut-2-ene,        1,1,2,3,4,4-hexafluorobut-2-ene, 1,1,1,3,4,4-hexafluorobut-2-ene        and 1,1,1,2,4,4-hexafluorobut-2-ene.

State of the art vertical 3D NAND structures require very high aspectratios through alternating stacks of materials.

A need remains for new etch gas compositions for use in plasmaapplications to form high aspect ratio apertures.

Notation and Nomenclature

Certain abbreviations, symbols, and terms are used throughout thefollowing description and claims, and include:

As used herein, the term “etch” or “etching” refers to a plasma etchprocess (i.e., a dry etch process) in which ion bombardment acceleratesthe chemical reaction in the vertical direction so that verticalsidewalls are formed along the edges of the masked features at rightangles to the substrate (Manos and Flamm, Plasma Etching AnIntroduction, Academic Press, Inc. 1989 pp. 12-13). The etching processproduces apertures, such as vias, trenches, channel holes, gatetrenches, staircase contacts, capacitor holes, contact holes, etc., inthe substrate.

The term “pattern etch” or “patterned etch” refers to etching anon-planar structure, such as a patterned mask layer on a stack ofsilicon-containing layers. The term “mask” refers to a layer thatresists etching. The mask layer may be located above or below the layerto be etched.

The term “selectivity” means the ratio of the etch rate of one materialto the etch rate of another material. The term “selective etch” or“selectively etch” means to etch one material more than anothermaterial, or in other words to have a greater or less than 1:1 etchselectivity between two materials.

As used herein, the indefinite article “a” or “an” means one or more.

The standard abbreviations of the elements from the periodic table ofelements are used herein. It should be understood that elements may bereferred to by these abbreviations (e.g., S refers to sulfur, Si refersto silicon, H refers to hydrogen, etc.).

As used herein, the abbreviation “NAND” refers to a “Negated AND” or“Not AND” gate; the abbreviation “2D” refers to 2 dimensional gatestructures on a planar substrate; the abbreviation “3D” refers to 3dimensional or vertical gate structures, wherein the gate structures arestacked in the vertical direction; and the abbreviation “DRAM” refers toDynamic Random-Access Memory.

Please note that the Si-containing films, such as SiN and SiO, arelisted throughout the specification and claims without reference totheir proper stoichiometry. The silicon-containing layers may includepure silicon (Si) layers, such as crystalline Si, polysilicon (polySi orpolycrystalline Si), or amorphous silicon; silicon nitride (Si_(k)N_(l))layers; or silicon oxide (Si_(n)O_(m)) layers; or mixtures thereof,wherein k, l, m, and n, inclusively range from 1 to 6. Preferably,silicon nitride is Si_(k)N_(l), where k and l each range from 0.5 to1.5. More preferably silicon nitride is Si₁N₁. Preferably silicon oxideis Si_(n)O_(m), where n ranges from 0.5 to 1.5 and m ranges from 1.5 to3.5. More preferably, silicon oxide is SiO₂ or SiO₃. Thesilicon-containing layer could also be a silicon oxide based dielectricmaterial such as organic based or silicon oxide based low-k dielectricmaterials such as the Black Diamond II or III material by AppliedMaterials, Inc. The silicon-containing layers may also include dopants,such as B, C, P, As and/or Ge.

SUMMARY

Disclosed are methods for etching silicon-containing films. An etchinggas is introduced into a plasma reaction chamber containing asilicon-containing film on a substrate. The etching gas istrans-1,1,1,4,4,4-hexafluoro-2-butene;cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutene;hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane(1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-); orhexafluorocyclobutane (cis-1,1,2,2,3,4). An inert gas is introduced intothe plasma reaction chamber. Plasma is activated to produce an activatedetching gas capable of selectively etching the silicon-containing filmfrom the substrate. The disclosed methods may include one or more of thefollowing aspects:

-   -   the etching gas being trans-1,1,1,4,4,4-hexafluoro-2-butene;    -   the etching gas being cis-1,1,1,4,4,4-hexafluoro-2-butene;    -   the etching gas being hexafluoroisobutene;    -   the etching gas being hexafluorocyclobutane (trans-1,1,2,2,3,4);    -   the etching gas being pentafluorocyclobutane (1,1,2,2,3-);    -   the etching gas being tetrafluorocyclobutane (1,1,2,2-);    -   the etching gas being hexafluorocyclobutane (cis-1,1,2,2,3,4);    -   the activated etching gas selectively reacting with the        silicon-containing film to form volatile by-products;    -   removing volatile by-products from the plasma reaction chamber;    -   the inert gas being selected from the group consisting of He,        Ar, Xe, Kr, and Ne;    -   the inert gas being Ar;    -   mixing the etching gas and the inert gas prior to introduction        to the plasma reaction chamber to produce a mixture;    -   introducing the etching gas into the plasma reaction chamber        separately from the inert gas;    -   introducing the inert gas continuously into the plasma reaction        chamber and introducing the etching gas into the plasma reaction        chamber in pulses;    -   the inert gas comprising approximately 50% v/v to approximately        95% v/v of a total volume of etching gas and inert gas        introduced into the plasma reaction chamber;    -   introducing an oxidizer into the plasma reaction chamber;    -   not introducing an oxidizer into the plasma reaction chamber;    -   the oxidizer being selected from the group consisting of O₂, CO,        CO₂, NO, N₂O, and NO₂;    -   the oxidizer being O₂;    -   mixing the etching gas and the oxidizer prior to introduction        into the plasma reaction chamber;    -   introducing the etching gas into the plasma reaction chamber        separately from the oxidizer;    -   introducing the oxidizer continuously into the plasma reaction        chamber and introducing the etching gas into the plasma reaction        chamber in pulses;    -   the oxidizer comprising approximately 5% v/v to approximately        100% v/v of a total volume of etching gas and oxidizer        introduced into the plasma reaction chamber;    -   the silicon-containing film comprising a layer of silicon oxide,        silicon nitride, polysilicon, or combinations thereof;    -   the silicon-containing film comprising oxygen atoms, nitrogen        atoms, carbon atoms, or combinations thereof;    -   the silicon-containing film not comprising silicon carbide;    -   the silicon-containing film being selectively etched from an        amorphous carbon layer;    -   the silicon-containing film being selectively etched from a        photoresist layer;    -   the silicon-containing film being selectively etched from a        polysilicon layer;    -   the silicon-containing film being selectively etched from a        metal contact layer;    -   the silicon-containing film being a silicon oxide layer;    -   the silicon oxide layer being a porous SiCOH film;    -   selectively etching the silicon oxide layer from an amorphous        carbon layer;    -   selectively etching the silicon oxide layer from a photoresist        layer;    -   selectively etching the silicon oxide layer from a polysilicon        layer;    -   selectively etching the silicon oxide layer from a metal contact        layer;    -   selectively etching the silicon oxide layer from a SiN layer;    -   the silicon-containing film being a silicon nitride layer;    -   selectively etching the silicon nitride layer from an amorphous        carbon layer;    -   selectively etching the silicon nitride layer from a patterned        photoresist layer;    -   selectively etching the silicon nitride layer from a polysilicon        layer;    -   selectively etching the silicon nitride layer from a metal        contact layer;    -   selectively etching the silicon nitride layer from a SiO layer;    -   selectively etching both silicon oxide and silicon nitride from        a silicon layer;    -   producing an aperture in the silicon-containing film having an        aspect ratio between approximately 10:1 and approximately 100:1;    -   producing a gate trench;    -   producing a staircase contact;    -   producing a channel hole;    -   producing a channel hole having an aspect ratio between        approximately 60:1 and approximately 100:1;    -   producing a channel hole having a diameter ranging from        approximately 40 nm to approximately 50 nm;    -   improving selectivity by introducing a second gas into the        plasma reaction chamber;    -   the second gas being selected from the group consisting of        cC₄F₈, C₄F₆, CF₄, CHF₃, CFH₃, CH₂F₂, COS, CS₂, CF₃I, C₂F₃I,        C₂F₅I, and SO₂.    -   the second gas being cC₅F₈;    -   the second gas being cC₄F₈;    -   the second gas being C₄F₆;    -   mixing the etching gas and the second gas prior to introduction        to the plasma reaction chamber;    -   introducing the etching gas into the plasma reaction chamber        separately from the second gas;    -   introducing approximately 1% v/v to approximately 99.9% v/v of        the second gas into the chamber;    -   activating the plasma by a RF power ranging from approximately        25 W to approximately 10,000 W;    -   the plasma reaction chamber having a pressure ranging from        approximately 1 mTorr to approximately 10 Torr;    -   introducing the etching gas to the plasma reaction chamber at a        flow rate ranging from approximately 5 sccm to approximately 1        slm;    -   maintaining the substrate at a temperature ranging from        approximately −196° C. to approximately 500° C.;    -   maintaining the substrate at a temperature ranging from        approximately −120° C. to approximately 300° C.;    -   maintaining the substrate at a temperature ranging from        approximately −10° C. to approximately 40° C.;    -   measuring the activated etching gas by Quadropole mass        spectrometer, optical emission spectrometer, FTIR, or other        radical/ion measurement tool;    -   generating the plasma by applying RF power.

Also disclosed are plasma etching compounds selected fromtrans-1,1,1,4,4,4-hexafluoro-2-butene;cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutene;hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane(1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-); orhexafluorocyclobutane (cis-1,1,2,2,3,4). The plasma etching compound hasa purity of at least 99.9% by volume and less than 0.1% by volume tracegas impurities. A total content of nitrogen-containing andoxygen-containing gas contained in said trace gaseous impurities is lessthan 150 ppm by volume. The disclosed plasma etching compounds mayinclude one or more of the following aspects:

-   -   the etching compound being        trans-1,1,1,4,4,4-hexafluoro-2-butene;    -   the etching compound being cis-1,1,1,4,4,4-hexafluoro-2-butene;    -   the etching compound being hexafluoroisobutene;    -   the etching compound being hexafluorocyclobutane        (trans-1,1,2,2,3,4);    -   the etching compound being pentafluorocyclobutane (1,1,2,2,3-);    -   the etching compound being tetrafluorocyclobutane (1,1,2,2-);    -   the etching compound being hexafluorocyclobutane        (cis-1,1,2,2,3,4);    -   the oxygen-containing gas being water;    -   the oxygen-containing gas being CO₂;    -   the nitrogen-containing gas being N₂; and    -   the plasma etching compound having a water content of less than        20 ppm by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like elements are given the same or analogous reference numbersand wherein:

FIG. 1 is the structural formula fortrans-1,1,1,4,4,4-hexafluoro-2-butene;

FIG. 2 is the structural formula forcis-1,1,1,4,4,4-hexafluoro-2-butene;

FIG. 3 is the structural formula fortrans-1,1,2,2,3,4-hexafluorocyclobutane;

FIG. 4 is the structural formula forcis-1,1,2,2,3,4-hexafluorocyclobutane;

FIG. 5 is the structural formula for hexafluoroisobutene;

FIG. 6 is the structural formula for 1,1,1,2,4,4,4-heptafluoro-2-butene;

FIG. 7 is the structural formula for 1,1,2,2,3-pentafluorocyclobutane;

FIG. 8 is the structural formula for 1,1,2,2-tetrafluorocyclobutane;

FIG. 9 is a diagram showing exemplary layers in a 3D NAND stack;

FIG. 10 is a diagram showing exemplary layers in a DRAM stack;

FIG. 11 is a mass spectrometry (MS) graph plotting the volume of speciesfractions produced by C₄F₆H₂ versus energy (in eV);

FIG. 12 is a MS graph plotting the volume of species fractions producedby C₄F₈ versus energy;

FIG. 13 is a MS graph plotting the volume of species fractions producedby trans-1,1,1,4,4,4-hexafluoro-2-butene versus energy;

FIG. 14 is a MS graph plotting the volume of species fractions producedby hexafluoroisobutene versus energy;

FIG. 15 is a graph of the SiO₂ etch rate versus oxygen flow (in sccm)for trans-1,1,2,2,3,4-hexafluorocyclobutane;

FIG. 16 is a graph of the SiO₂ etch rate versus oxygen flow for cC₄F₅H₃;

FIG. 17 is a graph of the selectivity versus oxygen flow fortrans-1,1,2,2,3,4-hexafluorocyclobutane;

FIG. 18 is a graph of the selectivity versus oxygen flow for cC₄F₅H₃;

FIG. 19 is a scanning electron micrograph (SEM) of the results of a 10minute etch using 15 sccm of cC₄F₈ and no oxygen;

FIG. 20 is a SEM of the results of a 10 minute etch using 15 sccm ofcC₄F₆H₂ and 12 sccm oxygen;

FIG. 21 is a SEM of the results of a 10 minute etch using 15 sccm ofcC₄F₅H₃ and 22 sccm oxygen; and

FIG. 22 is a flow chart showing the effect of H substitution, doublebonds, and addition of O to a C₄F₈ molecule.

DESCRIPTION OF PREFERRED EMBODIMENTS

Etching gases are disclosed for plasma etching channel holes, gatetrenches, staircase contacts, capacitor holes, contact holes, etc., insilicon-containing layers. The disclosed etching gases may providehigher selectivity to mask layers and no profile distortion in highaspect ratio structures.

The plasma etching gases may provide improved selectivity between theSi-containing layers and mask materials, less damage to channel region,and reduced bowing in pattern high aspect ratio structures. The plasmaetching gases may also etch through alternating layers of polySi, SiO,and/or SiN, resulting in a vertical etch profile.

The following compounds form the disclosed plasma etching gases:trans-1,1,1,4,4,4-hexafluoro-2-butene;cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutene;hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane(1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-); orhexafluorocyclobutane (cis-1,1,2,2,3,4). These compounds arecommercially available.

The disclosed plasma etching gases are provided at greater than 99.9%v/v purity, preferably at greater than 99.99% v/v purity, and morepreferably at greater than 99.999% v/v purity. The disclosed etchinggases contain less than 0.1% by volume trace gas impurities with lessthan 150 ppm by volume of nitrogen-containing and oxygen-containinggases, such as N₂ and/or H₂O and/or CO₂, contained in said trace gaseousimpurities. Preferably, the water content in the plasma etching gas isless than 20 ppm by weight. The purified product may be produced bydistillation and/or passing the gas or liquid through a suitableadsorbent, such as a 4A molecular sieve.

In one embodiment the disclosed plasma etching gas contains less than 5%v/v, preferably less than 1% v/v, more preferably less than 0.1% v/v,and even more preferably less than 0.01% v/v of any of its isomers. Thisembodiment may provide better process repeatability. This embodiment maybe produced by distillation of the gas or liquid. In an alternateembodiment, the disclosed plasma etching gas may contain between 5% v/vand 50% v/v of one or more of its isomers, particularly when the isomermixture provides improved process parameters or isolation of the targetisomer is too difficult or expensive. For example, a mixture of isomersmay reduce the need for two or more gas lines to the plasma reactor.

FIG. 1 is the structural formula fortrans-1,1,1,4,4,4-hexafluoro-2-butene. The CAS number fortrans-1,1,1,4,4,4-hexafluoro-2-butene is 66711-86-2.Trans-1,1,1,4,4,4-hexafluoro-2-butene has a boiling point of 8.5° C.

FIG. 2 is the structural formula forcis-1,1,1,4,4,4-hexafluoro-2-butene. The CAS number forcis-1,1,1,4,4,4-hexafluoro-2-butene is 692-49-9.Cis-1,1,1,4,4,4-hexafluoro-2-butene has a boiling point of 33° C.

FIG. 3 is the structural formula fortrans-1,1,2,2,3,4-hexafluorocyclobutane. The CAS number fortrans-1,1,2,2,3,4-hexafluorocyclobutane is 23012-94-4.Trans-1,1,2,2,3,4-hexafluorocyclobutane has a boiling point of 27° C.

FIG. 4 is the structural formula forcis-1,1,2,2,3,4-hexafluorocyclobutane. The CAS number forcis-1,1,2,2,3,4-hexafluorocyclobutane is 22819-47-2.Cis-1,1,2,2,3,4-hexafluorocyclobutane has a boiling point of 63° C.

FIG. 5 is the structural formula for hexafluoroisobutene. The CAS numberfor hexafluoroisobutene is 382-10-5. Hexafluoroisobutene has a boilingpoint of 14.5° C.

FIG. 6 is the structural formula for 1,1,1,2,4,4,4-heptafluoro-2-butene.The CAS number for 1,1,1,2,4,4,4-heptafluoro-2-butene is 760-42-9.1,1,1,2,4,4,4-heptafluoro-2-butene has a boiling point of 8° C.

FIG. 7 is the structural formula for 1,1,2,2,3-pentafluorocyclobutane.The CAS number for 1,1,2,2,3-pentafluorocyclobutane is 2253-02-3.1,1,2,2,3-pentafluorocyclobutane has a boiling point of 53° C.

FIG. 8 is the structural formula for 1,1,2,2-tetrafluorocyclobutane. TheCAS number for 1,1,2,2-tetrafluorocyclobutane is 374-12-9.1,1,2,2-tetrafluorocyclobutane has a boiling point of 50° C.

Some of these compounds are gaseous at room temperature and atmosphericpressure. For the non-gaseous (i.e., liquid) compounds, the gas form maybe produced by vaporizing the compounds through a conventionalvaporization step, such as direct vaporization or by bubbling. Thecompound may be fed in liquid state to a vaporizer where it is vaporizedbefore it is introduced into the reactor. Alternatively, the compoundmay be vaporized by passing a carrier gas into a container containingthe compound or by bubbling the carrier gas into the compound. Thecarrier gas may include, but is not limited to, Ar, He, N₂, and mixturesthereof. Bubbling with a carrier gas may also remove any dissolvedoxygen present in the etching gases. The carrier gas and compound arethen introduced into the reactor as a vapor.

If necessary, the container containing the compound may be heated to atemperature that permits the compound to have a sufficient vaporpressure for delivery into the etching tool. The container may bemaintained at temperatures in the range of, for example, approximately25° C. to approximately 100° C., preferably from approximately 25° C. toapproximately 50° C. More preferably, the container is maintained atroom temperature (˜25° C.) in order to avoid heating the lines to theetch tool. Those skilled in the art recognize that the temperature ofthe container may be adjusted in a known manner to control the amount ofcompound vaporized.

The disclosed etching gases are suitable for plasma etching channelholes, gate trenches, staircase contacts, capacitor holes, contactholes, etc., in one or more Si-containing layers and compatible with thecurrent and future generation of mask materials because they inducelittle to no damage on the mask along with good profile of high aspectratio structures. In order to achieve those properties, the disclosedetch gases may deposit an etch-resistant polymer layer during etching tohelp reduce the direct impact of the oxygen and fluorine radicals duringthe etching process. The disclosed compounds may also reduce damage topoly-Si channel structure during etching (see US 2011/0180941 to Hwanget al.). Preferably, the etching gas is both suitably volatile andstable during the etching process for delivery into the reactor/chamber.

The disclosed etching gases may be used to plasma etchsilicon-containing layers on a substrate. The disclosed plasma etchingmethod may be useful in the manufacture of semiconductor devices such asNAND or 3D NAND gates or Flash or DRAM memory. The disclosed etchinggases may be used in other areas of applications, such as differentfront end of the line (FEOL) and back end of the line (BEOL) etchapplications. Additionally, the disclosed etching gases may also be usedfor etching Si in 3D TSV (Through Silicon Via) etch applications forinterconnecting memory substrates on logic substrates.

The plasma etching method includes providing a plasma reaction chamberhaving a substrate disposed therein. The plasma reaction chamber may beany enclosure or chamber within a device in which etching methods takeplace such as, and without limitation, Reactive Ion Etching (RIE), DualCapacitively Coupled Plasma (CCP) with single or multiple frequency RFsources, Inductively Coupled Plasma (ICP), or Microwave Plasma reactors,or other types of etching systems capable of selectively removing aportion of the Si containing layer or generating active species. One ofordinary skill in the art will recognize that the different plasmareaction chamber designs provide different electron temperature control.Suitable commercially available plasma reaction chambers include but arenot limited to the Applied Materials magnetically enhanced reactive ionetcher sold under the trademark eMAX™ or the Lam Research Dual CCPreactive ion etcher Dielectric etch product family sold under thetrademark 2300® Flex™.

The plasma reaction chamber may contain one or more than one substrate.For example, the plasma reaction chamber may contain from 1 to 200silicon wafers having from 25.4 mm to 450 mm diameters. The one or moresubstrates may be any suitable substrate used in semiconductor,photovoltaic, flat panel or LCD-TFT device manufacturing. The substratewill have multiple films or layers thereon, including one or moresilicon-containing films or layers. The substrate may or may not bepatterned. Examples of suitable layers include without limitationsilicon (such as amorphous silicon, polysilicon, crystalline silicon,any of which may further be p-doped or n-doped with B, C, P, As, and/orGe), silica, silicon nitride, silicon oxide, silicon oxynitride,tungsten, titanium nitride, tantalum nitride, mask materials such asamorphous carbon, antireflective coatings, photoresist materials, orcombinations thereof. The silicon oxide layer may form a dielectricmaterial, such as an organic based or silicon oxide based low-kdielectric material (e.g., a porous SiCOH film). An exemplary low-kdielectric material is sold by Applied Materials under the trade nameBlack Diamond II or III. Additionally, layers comprising tungsten ornoble metals (e.g. platinum, palladium, rhodium or gold) may be used.

The substrate may include a stack of multiple silicon-containing layersthereon similar to those shown in FIGS. 9 and 10. In FIG. 9, a stack ofseven SiO/SiN layers are located on top of a silicon wafer substrate(i.e., ONON or TCAT technology). One of ordinary skill in the art willrecognize that some technologies replace the SiN layers with polySilayers (i.e., SiO/polySi layers in P-BICS technology). One of ordinaryskill in the art will further recognize that the number SiO/SiN orSiO/poly-Si layers in the 3D NAND stack may vary (i.e., may include moreor less than the seven SiO/SiN layers depicted). An amorphous carbonmask layer is located on top of the seven SiO/SiN layers. Anantireflective coating layer is located on top of the amorphous carbonmask. A pattern photoresist layer is located on top of theantireflective coating. The stack of layers in FIG. 9 reflects layerssimilar to those used in a 3D NAND gate. In FIG. 10, a thick SiO layeris located on top of a silicon wafer substrate. An amorphous carbon masklayer is located on top of the thick SiO layer. An antireflectivecoating layer is located on top of the amorphous carbon mask. A patternphotoresist layer is located on top of the antireflective coating. Thestack of layers in FIG. 10 reflects layers similar to those used in aDRAM gate. The disclosed etching gases selectively etch thesilicon-containing layers (i.e., SiO, SiN, polySi) more than theamorphous carbon mask, antireflective coating, or photoresist layers.Those layers may be removed by other etching gases in the same or adifferent reaction chamber. One of ordinary skill in the art willrecognize that the stack of layers in FIGS. 9 and 10 are provided forexemplary purposes only.

The disclosed etching gases are introduced into the plasma reactionchamber containing the substrate and silicon-containing layers. The gasmay be introduced to the chamber at a flow rate ranging fromapproximately 0.1 sccm to approximately 1 slm. For example, for a 200 mmwafer size, the gas may be introduced to the chamber at a flow rateranging from approximately 5 sccm to approximately 50 sccm.Alternatively, for a 450 mm wafer size, the gas may be introduced to thechamber at a flow rate ranging from approximately 25 sccm toapproximately 250 sccm. One of ordinary skill in the art will recognizethat the flow rate will vary from tool to tool.

An inert gas is also introduced into the plasma reaction chamber inorder to sustain the plasma. The inert gas may be He, Ar, Xe, Kr, Ne, orcombinations thereof. The etching gas and the inert gas may be mixedprior to introduction to the chamber, with the inert gas comprisingbetween approximately 50% v/v and approximately 95% v/v of the resultingmixture. Alternatively, the inert gas may be introduced to the chambercontinuously while the etching gas is introduced to the chamber inpulses.

The disclosed etching gas and inert gas are activated by plasma toproduce an activated etching gas. The plasma decomposes the etching gasinto radical form (i.e., the activated etching gas). The plasma may begenerated by applying RF or DC power. The plasma may be generated with aRF power ranging from about 25 W to about 10,000 W. The plasma may begenerated or present within the reactor itself. The plasma may begenerated in Dual CCP or ICP mode with RF applied at both electrodes. RFfrequency of plasma may range from 200 KHz to 1 GHz. Different RFsources at different frequency can be coupled and applied at sameelectrode. Plasma RF pulsing may be further used to control moleculefragmentation and reaction at substrate. One of skill in the art willrecognize methods and apparatus suitable for such plasma treatment.

Quadropole mass spectrometer (QMS), optical emission spectrometer, FTIR,or other radical/ion measurement tools may measure the activated etchinggas to determine the types and numbers of species produced. Ifnecessary, the flow rate of the etching gas and/or the inert gas may beadjusted to increase or decrease the number of radical species produced.

The disclosed etching gases may be mixed with other gases either priorto introduction into the plasma reaction chamber or inside the plasmareaction chamber. Preferably, the gases may be mixed prior tointroduction to the chamber in order to provide a uniform concentrationof the entering gas. In another alternative, the etching gas may beintroduced into the chamber independently of the other gases such aswhen two or more of the gases react. In another alternative, the etchinggas and the inert gas are the only two gases that are used during theetching process.

Exemplary other gases include, without limitation, oxidizers such as O₂,O₃, CO, CO₂, NO, N₂O, NO₂, and combinations thereof. The disclosedetching gases and the oxidizer may be mixed together prior tointroduction into the plasma reaction chamber. Alternatively, theoxidizer may be introduced continuously into the chamber and the etchinggas introduced into the chamber in pulses. The oxidizer may comprisebetween approximately 5% v/v to approximately 100% v/v of the mixtureintroduced into the chamber (with 100% v/v representing introduction ofpure oxidizer for the continuous introduction alternative).

Other exemplary gases with which the etching gas may be mixed includeadditional etching gases, such as cC₄F₈, C₄F₆, CF₄, CHF₃, CFH₃, CH₂F₂,COS, CS₂, CF₃I, C₂F₃I, C₂F₅I, and SO₂. The vapor of the etching gas andthe additional gas may be mixed prior to introduction to the plasmareaction chamber. The additional etching gas may comprise betweenapproximately 1% v/v to approximately 99.9% v/v of the mixtureintroduced into the chamber.

The Si-containing layers and the activated etching gas react to formvolatile by-products that are removed from the plasma reaction chamber.The amorphous carbon mask, antireflective coating, and photoresist layerare less reactive with the activated etching gas.

The temperature and the pressure within the plasma reaction chamber areheld at conditions suitable for the silicon-containing layer to reactwith the activated etching gas. For instance, the pressure in thechamber may be held between approximately 0.1 mTorr and approximately1000 Torr, preferably between approximately 1 mTorr and approximately 10Torr, more preferably between approximately 10 mTorr and approximately 1Torr, and more preferably between approximately 10 mTorr andapproximately 100 mTorr, as required by the etching parameters.Likewise, the substrate temperature in the chamber may range betweenabout approximately −196° C. to approximately 500° C., preferablybetween −120° C. to approximately 300° C., and more preferably between−10° C. to approximately 40° C. Chamber wall temperatures may range fromapproximately −196° C. to approximately 300° C. depending on the processrequirements.

The reactions between the Si-containing layer and the activated etchinggas results in anisotropic removal of the Si-containing layers from thesubstrate. Atoms of nitrogen, oxygen, and/or carbon may also be presentin the Si-containing layer. The removal is due to a physical sputteringof Si-containing layer from plasma ions (accelerated by the plasma)and/or by chemical reaction of plasma species to convert Si to volatilespecies, such as SiF_(x), wherein x ranges from 1-4.

The activated etching gas preferably exhibits high selectivity towardthe mask and etches through the alternating layers of SiO and SiNresulting in a vertical etch profile with no bowing, which is importantfor 3D NAND applications. For other applications, such as DRAM and 2DNAND, for example, the plasma activated etching gas may selectively etchSiO from SiN. The plasma activated etching gas preferably selectivelyetches SiO and/or SiN from mask layers, such as amorphous carbon,photoresist, polysilicon, or silicon carbide; or from metal contactlayers, such as Cu; or from channel regions consisting of SiGe orpolysilicon regions.

The disclosed etch processes using the disclosed etching gases producechannel holes, gate trenches, staircase contacts, capacitor holes,contact holes, etc., in the Si-containing layers. The resulting aperturemay have an aspect ratio ranging from approximately 10:1 toapproximately 100:1 and a diameter ranging from approximately 40 nm toapproximately 50 nm. For example, one of ordinary skill in the art willrecognize that a channel hole etch produces apertures in theSi-containing layers having an aspect ratio greater than 60:1.

In one non-limiting exemplary plasma etch process,trans-1,1,1,4,4,4-hexafluoro-2-butene is introduced into a 200 mm DualCCP plasma etch tool using a controlled gas flow device. The controlledgas flow device may be a mass flow controller. In case of high boilingpoint molecules, a special low pressure drop mass flow controller fromBrooks Automation (No. GF120XSD), MKS Instruments, etc., may be used.The pressure of the plasma reaction chamber is set at approximately 30mTorr. No gas source heating is necessary, as the vapor pressure of thiscompound is approximately 1340 torr at 25° C. The distance between thetwo CCP electrodes is kept at 1.35 cm and the top electrode RF power isfixed at 750 W. The bottom electrode RF power is varied to analyze theperformance of the molecule. The plasma reaction chamber contains asubstrate having 24 pairs of SiO and SiN layers thereon, similar tothose shown in FIG. 9. Prior to this process, the ARC layer is removedby a fluorocarbon and oxygen-containing gas and the APF layer is removedby an oxygen-containing gas. Argon is independently introduced into thechamber at a 250 sccm flow rate. Trans-1,1,1,4,4,4-hexafluoro-2-buteneis independently introduced into the chamber at 15 sccm. O₂ isindependently introduced into the chamber at 0-20 sccm to determineoptimum etching conditions. An aperture having an aspect ratio equal toor greater than 30:1 is produced, which may be used as a channel hole invertical NAND.

In another non-limiting exemplary plasma etch process,hexafluoroisobutene is introduced into a 200 mm Dual CCP plasma etchtool using a controlled gas flow device. The controlled gas flow devicemay be a mass flow controller. In case of high boiling point molecules,a special low pressure drop mass flow controller from Brooks Automation(No. GF120XSD), MKS Instruments, etc., may be used. The pressure of theplasma reaction chamber is set at approximately 30 mTorr. No gas sourceheating is necessary, as the vapor pressure of this compound isapproximately 900 Torr at 20° C. The distance between the two CCPelectrodes is kept at 1.35 cm and the top electrode RF power is fixed at750 W. The bottom electrode RF power is varied to analyze theperformance of the molecule. The plasma reaction chamber contains asubstrate having a thick SiO layer thereon, similar to the layer shownin FIG. 10. Prior to this process, the ARC layer is removed by afluorocarbon and oxygen-containing gas and the APF layer is removed byan oxygen-containing gas. Argon is independently introduced into thechamber at a 250 sccm flow rate. Hexafluoroisobutene is independentlyintroduced into the chamber at 15 sccm. O₂ is independently introducedinto the chamber at 0-20 sccm to determine optimum etching conditions.An aperture having an aspect ratio equal to or greater than 10:1 isproduced, which may be used as a contact hole in DRAM.

EXAMPLES

The following non-limiting examples are provided to further illustrateembodiments of the invention. However, the examples are not intended tobe all inclusive and are not intended to limit the scope of theinventions described herein.

The following testing was performed using the SAMCO10-NR reactive ionetcher (RIE) or the Lam 4520XLE™ advanced dielectric etch system (200 mmdual frequency capacitively coupled plasma (CCP) ion etch).

Example 1

C₄F₆ and cyclic C₄F₈ were directly injected into a quadruple massspectrometer (QMS) and data collected from 10-100 eV. The results areshown in FIGS. 11 and 12. Fragments from C₄F₆ have lower F:C ratio thanthe fragments from C₄F₈, which lead to higher polymer deposition rateand may improve selectivity.

Polymers were deposited by introduction into RIE plasma reaction chamberat 30 sccm with 1 sccm of Argon. The pressure in the chamber was set at5 Pa. The plasma was set at 300 W. Polymers were deposited from cC₄F₈ at100 nm/min and exhibited a 0.90 F:C ratio. Polymers were deposited fromC₄F₆ at 280 nm/min and exhibited a 0.76 F:C ratio. C₄F₆ exhibited a muchhigher depositions rate and the resulting film showed a lower F:C ratioin the polymer, which may indicate increased cross-linking.

Example 2

Polymers were deposited from cyclic C₄F₆H₂ and cyclic C₄F₅H₃ under thesame conditions as in Example 1 (i.e., 30 sccm etching gas, 1 sccm Ar, 5Pa and 300 W). cyclic C₄F₆H₂ and cyclic C₄F₅H₃ are similar to cyclicC₄F₈, but have replaced 2 or 3 F atoms with H. Polymers were depositedfrom cyclic C₄F₆H₂ at 150 nm/min and exhibited a 0.59 F:C ratio.Polymers were deposited from cyclic C₄F₅H₃ at 200 nm/min and exhibited a0.50 F:C ratio. Increasing the hydrogen content on the cyclic butanemolecule resulted in increased polymer deposition rates and a decreasedF:C ratio in the resulting polymer.

Example 3

Two molecules having the same stoichiometry (i.e., C₄F₆H₂) were directlyinjected into a quadruple mass spectrometer (QMS) and data collectedfrom 10-100 eV. The results for trans-1,1,1,4,4,4-hexafluoro-2-butene(CAS No 66711-86-2) are shown in FIG. 13. The results forhexafluoroisobutene (CAS No 382-10-5) are shown in FIG. 14. At higherenergies, more CF₃ fragments and less C₃F₃H₂ fragments were producedfrom hexafluoroisobutene than fromtrans-1,1,1,4,4,4-hexafluoro-2-butene. Fragments from C₄F₆ have lowerF:C ratio than the fragments for C₄F₈, which lead to higher polymerdeposition rate and may improve selectivity.

Polymers were deposited from both C₄F₆H₂ compounds under the sameconditions as in Example 1 (i.e., 30 sccm etching gas, 1 sccm Ar, 5 Paand 300 W). Polymers were deposited fromtrans-1,1,1,4,4,4-hexafluoro-2-butene at 250 nm/min and exhibited a 0.53F:C ratio. Polymers were deposited from cyclic hexafluoroisobutene at220 nm/min and exhibited a 0.53 F:C ratio.

Example 4

The following table summarizes test results for multiple etching gases:

TABLE 1 2^(nd) Polymer 1^(st) fragment fragment Dep F:C Molecule¹ H C═Cat 100 ev at 100 ev Rate² Polymer cC₄F₈ No No C₂F₄ C₃F₅ 100 0.90 C₄F₆ NoYes C₃F₃ CF 280 0.76 66711-86-2 Yes Yes C₃H₂F₃ CF₃ 250 0.53 382-10-5 YesYes CF₃ C₃H₂F₃ 220 0.53 C₄F₈ No Yes C₃F₅ CF₃ 100 1.00 22819-47-2 Yes NoC₂HF₃ C₃H₂F₃ 150 0.59 23102-94-4 Yes No C₂HF₃ C₃H₂F₃ 120 0.58 2253-02-3Yes No C₃F₃ CF 200 0.50 ¹cC₄F₈ = octafluorocyclobutane; C₄F₆ =hexafluorobutadiene, C₄F₈ = octafluoro-2-butene ²30 sccm etching gas, 1sccm Ar, 5 Pa and 300 WBased on these results, the lowest polymer deposition rates showed thehighest F:C ratio in the resulting polymer (cC₄F₈ and C₄F₈). The largedifference in polymer deposition rates (in nm/min) between the fourmolecules having double bonds (i.e., rows 2-5) illustrates thatinclusion of double bonds does not exclusively control polymerization.Instead, the deposition rate more closely followed fragmentation. Inother words, molecules producing fragments having higher F:C ratios hadreduced polymer deposition rates.

Example 5

The effect of increasing H on SiO₂ etch rate was analyzed. A graph ofthe SiO₂ etch rate versus oxygen flow (in sccm) fortrans-1,1,2,2,3,4-hexafluorocyclobutane is shown in FIG. 15. A graph ofthe SiO₂ etch rate versus oxygen flow for cC₄F₅H₃ is shown in FIG. 16.Replacing one F with H resulted in higher oxygen flow rates and narrowerprocess windows.

The effect of increasing H on oxide selectivity versus amorphous carbon(a-C), photoresist (PR), and nitride was also analyzed. A graph of theselectivity versus oxygen flow fortrans-1,1,2,2,3,4-hexafluorocyclobutane is provide in FIG. 17. A graphof the selectivity versus oxygen flow for cC₄F₅H₃ is shown in FIG. 18.The molecule flow rates in FIGS. 17 and 18 are the same as those inFIGS. 15 and 16 (i.e., the square data on the left is from 5 sccm etchgas flow rate, the diamond data second from left is 10 sccm, thetriangle data second from right is 15 sccm, and the circle data right is20 sccm). In FIGS. 17 and 18, the solid symbols represent the siliconoxide/photoresist selectivity, the hollow symbols represent the siliconoxide/silicon nitride selectivity, and the shaded symbols represent thesilicon oxide/amorphous carbon selectivity.

Example 6

The following table summarizes test results for multiple etching gases:

TABLE 2 Molecule³ H C═C PR a-C N O₂/gas ratio cC₄F₈ No No 3.0 5.0 3.2 0C₄F₆ No Yes 1.1 4.3 2.3 1.5 66711-86-2 Yes Yes 2.2 9.9 1.5 1.5 382-10-5Yes Yes 1.0 2.7 0.6 1.7 C₄F₈ No Yes 2.8 6.9 5.1 0.2 22819-47-2 Yes No5.6 Inf 2.2 1.4 23102-94-4 Yes No 4.3 11.6 1.7 0.8 2253-02-3 Yes No InfInf Inf 1.5 ³cC₄F₈ = octafluorocyclobutane; C₄F₆ = hexafluorobutadiene,C₄F₈ = octafluoro-2-buteneThe molecules were compared under similar SiO₂ etch rate conditions (ER40-50 nm/mm). The etching gas and oxygen flow rates were selected forbest selectivity within the etch rate range. Other plasma conditionswere fixed (i.e., Ar=150 sccm, 300 W, 5 Pa). The PR, a-C and N columnsshow the selectivity between SiO₂ and photoresist (PR), amorphous carbon(a-C), and silicon nitride (N). Based on these results, and particularlythe results for cC₄F₈, 23102-94-4(trans-1,1,2,2,3,4-hexafluorocyclobutane), and 2253-02-3(1,1,2,2,3-pentafluorocyclobutane), increasing H increased maskselectivity. Additionally, even though 66711-86-2(trans-1,1,1,4,4,4-hexafluoro-2-butene) and 382-10-5(hexafluoroisobutene) have the same stoichiometry (i.e., C₄F₆H₂), thedifferent structures resulted in significantly different results.

Example 7

The effect of increased H content when etching a portion of a DRAMpattern stack was analyzed. The portion of the DRAM patterned stackconsisted of P6100 patterns (2.9 kÅ) on an antireflective coating layer(ARC29a—0.8 kÅ), on a silicon oxynitride layer (1.0 kÅ), on an amorphouscarbon layer (3.5 kÅ), on a 4 micron SiO₂ substrate (Silox). Argon wasintroduced at 150 sccm. The chamber was maintained at 5 Pa. The SAMCORIE was set at 300 W. A scanning electron micrograph of the results of a10 minute etch using 15 sccm of cC₄F₈ and no oxygen is provided in FIG.19. A scanning electron micrograph of the results of a 10 minute etchusing 15 sccm of cC₄F₆H₂ and 12 sccm oxygen is provided in FIG. 20. Ascanning electron micrograph of the results of a 10 minute etch using 15sccm of cC₄F₈H₃ and 22 sccm oxygen is provided in FIG. 21. As seen inthe figures, increasing H promotes a tapered profile and results in aloss of etch rate (590 nm→380 nm→270 nm). Increased H content maintaineda narrow trench. The 110 nm trench in FIG. 21 was present before theetch, whereas the trench was increased to 270 nm by cC₄F₆H₂ and 260 nmby cC₄F₈.

Example 8

FIG. 22 is a flow chart showing the effect of H substitution, doublebonds, and addition of O to a C₄F₈ molecule. C₄F₈ is shown in the topleft corner of FIG. 22. An increased selectivity between SiO and maskand increased polymer deposition rate is seen when replacing 2 or 3 Fatoms with hydrogen atoms (moving left to right along the top row).However, the increased H molecules also require an increase in O₂dilution. An increased polymer deposition rate but similar selectivityand O₂ dilution requirements are seen when two F atoms are replaced by adouble bond (i.e., changing the molecule from saturated to unsaturated)(moving from the middle of the first row to the right side of the secondrow). Addition of oxygen results in poor selectivity and no polymerdeposition (moving down the column on the left side of the page). Anincreased selectivity and polymer deposition rate is seen, but in anarrow process window, when fluorine atoms are replaced by hydrogenatoms on the oxygen-containing molecule (bottom left side of page).

Example 9

The deposition and etch rates for cyclic C₄F₈ (octafluorocyclobutane),C₄F₆ (hexafluoro-1,3-butadiene), and linear C₄F₆H₂ (CAS 66711-86-2) weremeasured.

The source or RF power of the Lam etch system was set at 750 W and thebias power was set at 1500 W. The pressure was set at 30 mTorr. Thedistance between the plates was set at 1.35 cm. Oxygen was introduced ata flow rate of 15 sccm. Argon was introduced at a flow rate of 250 sccm.Each etch gas was introduced at 15 sccm. The results are shown in thefollowing table:

TABLE 3 SiO2 Selectivity Selectivity Polymer Molecule⁴ Etch Rate a-C SiNDep Rate cC₄F₈ 440 4 2 56 C₄F₆ 501 8 — 467 66711-86-2 390 12 2 250⁴cC₄F₈ = octafluorocyclobutane; C₄F₆ = hexafluorobutadiene66711-86-2 (trans-1,1,1,4,4,4-hexafluoro-2-butene) has betterselectivity between silicon oxide and amorphous carbon than theconventional cC₄F₈, with a similar silicon oxide etch rate. 66711-86-2also has a higher deposition rate than cC₄F₈.

Example 10

The etch rate of SiO₂, SiN, p-Si (polysilicon), and a-C (amorphouscarbon) using 1,1,1,2,4,4,4-heptafluoro-2-butene was measured.

The source or RF power of the Lam etch system was set at 750 W and thebias power was set at 1500 W. The pressure was set at 30 mTorr. Thedistance between the plates was set at 1.35 cm. Oxygen was introduced ata flow rate of 15 sccm. Argon was introduced at a flow rate of 250 sccm.1,1,1,2,4,4,4-heptafluoro-2-butene was introduced at a flow rate of 15sccm. 1,1,1,2,4,4,4-heptafluoro-2-butene etched the SiO₂ layer at therate of 550 nm/mm. 1,1,1,2,4,4,4-heptafluoro-2-butene etched the SiNlayer at the rate of 150 nm/min. 1,1,1,2,4,4,4-heptafluoro-2-buteneetched the p-Si layer at the rate of 50 nm/mm.1,1,1,2,4,4,4-heptafluoro-2-butene etched the a-c layer at the rate of75 nm/min. 1,1,1,2,4,4,4-heptafluoro-2-butene shows good selectivitybetween SiO₂ and p-Si and a-c.

While embodiments of this invention have been shown and described,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit or teaching of this invention. The embodimentsdescribed herein are exemplary only and not limiting. Many variationsand modifications of the composition and method are possible and withinthe scope of the invention. Accordingly the scope of protection is notlimited to the embodiments described herein, but is only limited by theclaims which follow, the scope of which shall include all equivalents ofthe subject matter of the claims.

What is claimed is:
 1. A method of depositing a polymer layer, themethod comprising plasma activating a fluorocarbon molecule to form thepolymer layer, the fluorocarbon molecule selected from the groupconsisting of hexafluoroisobutene; pentafluorocyclobutane (1,1,2,2,3-);and tetrafluorocyclobutane (1,1,2,2-); and wherein the polymer layerforms a protection layer on sidewalls of a pattern etch structure. 2.The method of claim 1, the method further comprising no addition ofoxygen.
 3. The method of claim 1, wherein the pattern etch structure hasan aspect ratio ranging from 2.5:1 to 100:1.
 4. The method of claim 3,wherein the pattern etch structure has an aspect ratio ranging from 10:1to 100:1.
 5. The method of claim 1, wherein the polymer layer preventsions and radicals from etching the sidewalls.
 6. The method of claim 5,wherein the polymer layer results in a pattern etch structure having avertical profile that is straight with no bowing.
 7. A method ofproducing a pattern etch structure, the method comprising plasmaactivating a fluorocarbon molecule to form a polymer layer on a sidewallof the pattern etch structure, the fluorocarbon molecule selected fromthe group consisting of hexafluoroisobutene; pentafluorocyclobutane(1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-).
 8. The method of claim7, the method further comprising no addition of oxygen.
 9. The method ofclaim 7, wherein the pattern etch structure has an aspect ratio rangingfrom 2.5:1 to 100:1.
 10. The method of claim 9, wherein the pattern etchstructure has an aspect ratio ranging from 10:1 to 100:1.
 11. The methodof claim 7, the method further comprising the polymer layer preventingions and radicals from etching the sidewalls.
 12. The method of claim11, the pattern etch structure produced having a vertical profile thatis straight with no bowing.